Noninvasive Fluid Dynamic Power Loss Assessments for Total Cavopulmonary Connections Using the Viscous Dissipation Function: A Feasibility Study

2001 ◽  
Vol 123 (4) ◽  
pp. 317-324 ◽  
Author(s):  
Timothy M. Healy ◽  
Carol Lucas ◽  
Ajit P. Yoganathan
Keyword(s):  
Cardiac Output ◽  
Viscous Dissipation ◽  
Velocity Gradient ◽  
Power Loss ◽  
Control Volume ◽  
Fluid Dynamic ◽  
Dissipation Function ◽  
Power Losses ◽  
Dynamic Power ◽  
The Right

The total cavopulmonary connection (TCPC) has shown great promise as an effective palliation for single-ventricle congenital heart defects. However, because the procedure results in complete bypass of the right-heart, fluid dynamic power losses may play a vital role in postoperative patient success. Past research has focused on determining power losses using control volume methods. Such methods are not directly applicable clinically without highly invasive pressure measurements. This work proposes the use of the viscous dissipation function as a tool for velocity gradient based estimation of fluid dynamic power loss. To validate this technique, numerical simulations were conducted in a model of the TCPC incorporating a 13.34 mm (one caval diameter) caval offset and a steady cardiac output of 2 Ls˙min−1. Inlet flow through the superior vena cava was 40 percent of the cardiac output, while outflow through the right pulmonary artery (RPA) was varied between 30 and 70 percent, simulating different blood flow distributions to the lungs. Power losses were determined using control volume and dissipation function techniques applied to the numerical data. Differences between losses computed using these techniques ranged between 3.2 and 9.9 percent over the range of RPA outflows studied. These losses were also compared with experimental measurements from a previous study. Computed power losses slightly exceeded experimental results due to different inlet flow conditions. Although additional experimental study is necessary to establish the clinical applicability of the dissipation function, it is believed that this method, in conjunction with velocity gradient information derived from imaging modalities such as magnetic resonance imaging, can provide a noninvasive means of assessing power losses within the TCPC in vivo.

The Effect of Incorporating Vessel Compliance in a Computational Model of Blood Flow in a Total Cavopulmonary Connection (TCPC) with Caval Centerline Offset

2004 ◽  
Vol 126 (6) ◽  
pp. 709-713 ◽  
Author(s):  
J. C. Masters ◽  
M. Ketner ◽  
M. S. Bleiweis ◽  
M. Mill ◽  
A. Yoganathan ◽  
...  
Keyword(s):  
Blood Flow ◽  
Power Loss ◽  
Fluid Dynamic ◽  
Reducing Power ◽  
Pressure Head ◽  
Congenital Defects ◽  
Total Cavopulmonary Connection ◽  
Flow Mixing ◽  
The Right ◽  
Cavopulmonary Connection

Background—The total cavopulmonary connection (TCPC), a palliative correction for congenital defects of the right heart, is based on the corrective technique developed by Fontan and Baudet. Research into the TCPC has primarily focused on reducing power loss through the connection as a means to improve patient longevity and quality of life. The goal of our study is to investigate the efficacy of including a caval offset on the hemodynamics and, ultimately, power loss of a connection. As well, we will quantify the effect of vessel wall compliance on these factors and, in addition, the distribution of hepatic blood to the lungs. Methods—We employed a computational fluid dynamic model of blood flow in the TCPC that includes both the non-Newtonian shear thinning characteristics of blood and the nonlinear compliance of vessel tissue. Results—Power loss in the rigid-walled simulations decayed exponentially as caval offset increased. The compliant-walled results, however, showed that after an initial substantial decrease in power loss for offsets up to half the caval diameter, power loss increased slightly again. We also found only minimal mixing in both simulations of all offset models. Conclusions—The increase in power loss beyond an offset of half the caval diameter was due to an increase in the kinetic contribution. Reduced caval flow mixing, on the other hand, was due to the formation of a pressure head in the offset region which acts as a barrier to flow.

INFLUENCE OF EXERCISE ON THREE TYPES OF FONTAN MODIFICATIONS: COMPARISON BY NUMERICAL SIMULATIONS

2014 ◽  
Vol 14 (01) ◽  
pp. 1450007
Author(s):  
QI SUN ◽  
JINLONG LIU ◽  
HAIBO ZHANG ◽  
JINGHAO ZHENG ◽  
HAIFA HONG ◽  
...  
Keyword(s):  
Energy Efficiency ◽  
Flow Rate ◽  
Resting State ◽  
Power Loss ◽  
Control Volume ◽  
Vena Cava ◽  
Extracardiac Conduit ◽  
Cavopulmonary Anastomosis ◽  
Right Pulmonary Artery ◽  
The Right

Low energy efficiency of Fontan-type connections in exercise conditions may lead to limited post-operative exercise capacity of patients. The objective of this study was to compare the energy efficiency of different types of Fontan modifications in exercise conditions. In this study, the flow rate of the inferior vena cava (IVC) was increased artificially to simulate exercise conditions. The control volume power loss and energy efficiency were investigated in three types of Fontan modifications using the method of computational fluid dynamics (CFD). In the intracardiac tunnel Fontan, the power loss was 7.9 times of that calculated in resting state when the flow rate of IVC increased to three times of that measured at the right pulmonary artery flow ratio of 50%. The energy efficiency of it decreased prominently from 91.9% to 79.9%. On the contrary, in the extracardiac Fontan with direct cavopulmonary anastomosis (direct Fontan), the magnitude of power loss was only 2.9 times of that in resting state and the energy efficiency changed only from 91.8% to 89.1%. The results of extracardiac conduit Fontan fell in between. It showed that direct Fontan had higher energy efficiency than intracardiac tunnel or extracardiac conduit Fontan in exercise conditions.

The effect of viscous dissipation on natural convection in a square cavity

2019 ◽  
Vol 5 (3) ◽  
pp. 118-130 ◽  
Author(s):  
Pavel T. Zubkov ◽  
Eduard I. Narygin
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Viscous Dissipation ◽  
Convection Heat Transfer ◽  
Dissipation Function ◽  
Initial Condition ◽  
Square Cavity ◽  
Conservation Of Energy ◽  
Left Wall ◽  
The Right

This article studies the natural convection of a viscous, incompressible fluid in a square cavity in a gravitational field. The temperature of vertical walls is constant. The temperature of the left wall is higher than temperature of the right wall; the horizontal walls are considered thermally insulated. The initial condition for the temperature of a fluid in a square caviry is the constant and equals the temperature of the right wall. The initial condition for the velocity is zero. We consider only those cases where the obtained flow in the cavity is laminar. All thermophysical characteristics are assumed constant, except for one when the motion equation accounts for the gravity. Mathematical model is the Boussinesq approximation but the equation of conservation of energy contains Rayleigh dissipation function.<br> In this article, the authors have researched the effect of viscous dissipation on natural convection heat transfer in square field. The results show that viscous dissipation significantly affects the heat transfer through the cavity. This problem was solved with the finite volume method by algorithm SIMPLER for Pr=1, Gr=10<sup>4</sup>, and 10<sup>−5</sup>≤Ec≤10<sup>−3</sup>.

scholarly journals The Power Losses in Cable Lines Supplying Nonlinear Loads

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1374
Author(s):  
Bartosz Rozegnał ◽  
Paweł Albrechtowicz ◽  
Dominik Mamcarz ◽  
Monika Rerak ◽  
Maciej Skaza
Keyword(s):  
Bessel Function ◽  
Cross Section ◽  
Power Loss ◽  
Sine Wave ◽  
Active Power ◽  
New Method ◽  
Power Losses ◽  
Nonlinear Loads ◽  
Current Harmonics ◽  
Cable Lines

This paper presents the skin effect impact on the active power losses in the sheathless single-core cables/wires supplying nonlinear loads. There are significant conductor losses when the current has a distorted waveform (e.g., the current supplying diode rectifiers). The authors present a new method for active power loss calculation. The obtained results have been compared to the IEC-60287-1-1:2006 + A1:2014 standard method and the method based on the Bessel function. For all methods, the active power loss results were convergent for small-cable cross-section areas. The proposed method gives smaller power loss values for these cable sizes than the IEC and Bessel function methods. For cable cross-section areas greater than 185 mm2, the obtained results were better than those for the other methods. There were also analyses of extra power losses for distorted currents compared to an ideal 50 Hz sine wave for all methods. The new method is based on the current penetration depth factor calculated for every considered current harmonics, which allows us to calculate the precise equivalent resistance for any cable size. This research is part of our work on a cable thermal analysis method that has been developed.

scholarly journals Performance of a capnodynamic method estimating cardiac output during respiratory failure - before and after lung recruitment

2019 ◽  
Vol 34 (6) ◽  
pp. 1199-1207
Author(s):  
Thorir Svavar Sigmundsson ◽  
Tomas Öhman ◽  
Magnus Hallbäck ◽  
Eider Redondo ◽  
Fernando Suarez Sipmann ◽  
...  
Keyword(s):  
Cardiac Output ◽  
Respiratory Failure ◽  
Reference Method ◽  
Hemodynamic Instability ◽  
Lung Lavage ◽  
Lung Recruitment ◽  
Recruitment Manoeuvre ◽  
Percentage Error ◽  
Before And After ◽  
The Right

AbstractRespiratory failure may cause hemodynamic instability with strain on the right ventricle. The capnodynamic method continuously calculates cardiac output (CO) based on effective pulmonary blood flow (COEPBF) and could provide CO monitoring complementary to mechanical ventilation during surgery and intensive care. The aim of the current study was to evaluate the ability of a revised capnodynamic method, based on short expiratory holds (COEPBFexp), to estimate CO during acute respiratory failure (LI) with high shunt fractions before and after compliance-based lung recruitment. Ten pigs were submitted to lung lavage and subsequent ventilator-induced lung injury. COEPBFexp, without any shunt correction, was compared to a reference method for CO, an ultrasonic flow probe placed around the pulmonary artery trunk (COTS) at (1) baseline in healthy lungs with PEEP 5 cmH2O (HLP5), (2) LI with PEEP 5 cmH2O (LIP5) and (3) LI after lung recruitment and PEEP adjustment (LIPadj). CO changes were enforced during LIP5 and LIPadj to estimate trending. LI resulted in changes in shunt fraction from 0.1 (0.03) to 0.36 (0.1) and restored to 0.09 (0.04) after recruitment manoeuvre. Bias (levels of agreement) and percentage error between COEPBFexp and COTS changed from 0.5 (− 0.5 to 1.5) L/min and 30% at HLP5 to − 0.6 (− 2.3 to 1.1) L/min and 39% during LIP5 and finally 1.1 (− 0.3 to 2.5) L/min and 38% at LIPadj. Concordance during CO changes improved from 87 to 100% after lung recruitment and PEEP adjustment. COEPBFexp could possibly be used for continuous CO monitoring and trending in hemodynamically unstable patients with increased shunt and after recruitment manoeuvre.

An Entropy Based Evaluation of Efficiency of a Transonic Compressor Rotor With Water Injection

2008 ◽  
Author(s):  
Istvan Szabo ◽  
Mark G. Turner
Keyword(s):  
Viscous Dissipation ◽  
Entropy Generation ◽  
Dissipation Function ◽  
Entropy Generation Rate ◽  
Thermodynamic Efficiency ◽  
Compression Process ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Wet Compression ◽  
Isentropic Efficiency

Defining the thermodynamic efficiency of the wet compression process in a compressor is not trivial, since the flow in this case has multiple phases present which interact with each other. In this paper, an approach is presented that calculates the overall entropy creation and thus the isentropic efficiency of a wet compression process in a transonic compressor rotor. The viscous dissipation function is calculated everywhere in the domain in the post-processing phase of the CFD simulation and integrated to the wall, with special treatment in the near-wall regions where high rates of entropy generation occur. The isentropic efficiency of the wet compression is then determined from the entropy generation rate. Analytical integration of wall functions and numerical integration of the viscous dissipation function allows for reasonable results even with relatively coarse grids and can be applied for single-phase flows. The methodology presented is also useful to quantify the efficiency of thermodynamic processes in devices that introduce streams into the flow path, such as cooled turbines and compressors with flow control.

scholarly journals An Improved Particle Swarm Optimization Algorithm Using Eagle Strategy for Power Loss Minimization

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Hamza Yapıcı ◽  
Nurettin Çetinkaya
Keyword(s):  
Genetic Algorithm ◽  
Particle Swarm Optimization ◽  
Power System ◽  
Power Loss ◽  
Particle Swarm Optimization Algorithm ◽  
Reactive Power ◽  
Particle Swarm ◽  
Power Losses ◽  
Swarm Optimization ◽  
Eagle Strategy

The power loss in electrical power systems is an important issue. Many techniques are used to reduce active power losses in a power system where the controlling of reactive power is one of the methods for decreasing the losses in any power system. In this paper, an improved particle swarm optimization algorithm using eagle strategy (ESPSO) is proposed for solving reactive power optimization problem to minimize the power losses. All simulations and numerical analysis have been performed on IEEE 30-bus power system, IEEE 118-bus power system, and a real power distribution subsystem. Moreover, the proposed method is tested on some benchmark functions. Results obtained in this study are compared with commonly used algorithms: particle swarm optimization (PSO) algorithm, genetic algorithm (GA), artificial bee colony (ABC) algorithm, firefly algorithm (FA), differential evolution (DE), and hybrid genetic algorithm with particle swarm optimization (hGAPSO). Results obtained in all simulations and analysis show that the proposed method is superior and more effective compared to the other methods.

scholarly journals Parasitic-Based Active Gate Driver Improving the Turn-On Process of 1.7 kV SiC Power MOSFET

2021 ◽  
Vol 11 (5) ◽  
pp. 2210
Author(s):  
Bartosz Lasek ◽  
Przemysław Trochimiuk ◽  
Rafał Kopacz ◽  
Jacek Rąbkowski
Keyword(s):  
Gate Voltage ◽  
Drain Current ◽  
Theoretical Background ◽  
Dissipated Energy ◽  
Feedback Signal ◽  
Power Losses ◽  
Turn On ◽  
Speed Up ◽  
Gate Driver ◽  
The Right

This article discusses an active gate driver for a 1.7 kV/325 A SiC MOSFET module. The main purpose of the driver is to adjust the gate voltage in specified moments to speed up the turn-on cycle and reduce the amount of dissipated energy. Moreover, an adequate manipulation of the gate voltage is necessary as the gate current should be reduced during the rise of the drain current to avoid overshoots and oscillations. The gate voltage is switched at the right moments on the basis of the feedback signal provided from a measurement of the voltage across the parasitic source inductance of the module. This approach simplifies the circuit and provides no additional power losses in the measuring circuit. The paper contains the theoretical background and detailed description of the active gate driver design. The model of the parasitic-based active gate driver was verified using the double-pulse procedure both in Saber simulations and laboratory experiments. The active gate driver decreases the turn-on energy of a 1.7 kV/325 A SiC MOSFET by 7% comparing to a conventional gate driver (VDS = 900 V, ID = 270 A, RG = 20 Ω). Furthermore, the proposed active gate driver lowered the turn-on cycle time from 478 to 390 ns without any serious oscillations in the main circuit.

Chronic isolation of carotid sinus baroreceptor region in conscious normotensive and hypertensive rats

1998 ◽  
Vol 275 (1) ◽  
pp. H322-H329 ◽  
Author(s):  
Kelly P. McKeown ◽  
Artin A. Shoukas
Keyword(s):  
Heart Rate ◽  
Cardiac Output ◽  
Arterial Pressure ◽  
Carotid Sinus ◽  
Baroreceptor Reflex ◽  
Hypertensive Rats ◽  
Conscious Rat ◽  
Sd Rats ◽  
The Right ◽  
Reflex System

We have developed a chronic technique to isolate the carotid sinus baroreceptor region in the conscious rat model. Our technique, when used in conjunction with other methods, allows for the study of the control of arterial pressure, heart rate, and cardiac output by the carotid sinus baroreceptor reflex in conscious, unrestrained rats. The performance of our technique was evaluated in two strains: normotensive Sprague-Dawley (SD) rats and spontaneously hypertensive rats (SHR). Each rat was instrumented with an aortic flow probe and a catheter placed in the right femoral artery to monitor cardiac output and arterial pressure, respectively. The cervical sympathetic trunk and aortic depressor nerve were ligated and cut bilaterally, leaving vagus nerves intact. The right and left carotid sinuses were isolated using our new technique. We tested the open-loop function of the carotid sinus baroreceptor reflex system in the conscious rat after recovery from the isolation surgery. We found that changes in nonpulsatile carotid sinus pressure caused significant changes in arterial pressure, heart rate, and total peripheral resistance in both rat strains. However, the cardiac output responses differed dramatically between strains. Significant changes were seen in the cardiac output response of SHR, whereas no significant changes were observed in normotensive SD rats. We have found this technique to be a highly reliable tool for the study of the carotid sinus baroreceptor reflex system in the conscious rat.

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